Switching apparatus for sound-reproducing systems



. SWITCHING APPARATUS FOR SOUND REPROI JUCING SYSTEMS Filed April 1, 1927 2 Sheets-Sheet 1 I 20 AL; [W

2/ \rI-E I I l 1/ A1 I /.9 r 27 G M1 200:

we 7 9 SHIV J M 17 I *===L=== I A ttorney Jan. 13, 1931. J. REYNOLDS 88,

SWITCHING APPARATUS FOR SOUND REPRODUCING SYSTEMS Filed April 1, 1927 2 Sheets-Sheet 2 0/ Inventor 5, flw g .4 ttomev Patented Jan. 13, 1931 UNITED STATES PATENT OFFICE JOHN LOUIS REYNOLDS, OF LONG ISLAND CITY, NEW YORK, ASSIGNOR, BY MESFI'E AS- SIGMENTS, TO ELECTRICAL RESEARCH PRODUCTS INC., A CORPORATION OF DELA- WARE SWITCHING APPARATUS FOR SOOND-BEPRODUGING SYSTEMS Application filed April 1, 1927. Serial No. 180,324.

This invention relates to transmitting and reproducing systems and in particular to -methods and means for rapidly efiecting switching operations in such systems.

The invention is eminently useful in socalled synchronized sound and moving plcture systems, especially where the sound and desirable in the switch-over from one record to another that there be produced no deleterious eifects on the sound' reproduction that might be perceptible to an audience.

()ne of the principal objects of the invention is to provide a method of effectively associating each of a plurality of sound translating devices in succession with a single reproducer in such a manner that the substituting of one record for another is accomplished in a rapid and smooth manner.

A feature of the invention resides in the means for connecting in succession a number of sources of sound modulated currents with an electric current amplifier without causing disconnection of said amplifiers from either of said sources.

Another feature of the invention is embodied in a potentiometer or variable network which is permanently connected between a number of sound translators and an electron discharge amplifier of fixed gain, so that movement of the switcharm of said potentiometer or network serves to place said amplifier under control of a single one of said translators, and at the same time to control the energy level of the currents applied to the amplifier.

A still further feature of the invention pertains to a combination of electrical resistances and switching means therefor for associating the input circuit of an electron discharge amplifier with an electrical pickup device so that the impedances of the circuits facing toward the amplifier and toward the pickup device are the same independently of the position of the switchlng means.

Other features and advantages not specifically enumerated in become apparent upon a consideration 0 the descriptions given hereinbelow and as set forth in the appended claims.

Accordingly, for the purpose of illustrating one manner of attaining the above objects and features, as Well as for the purpose of making the invention clear, it has been chosen to illustrate the same as applied to sound recording and reproducing apparatus. However, it is understood that the inventive idea is capable of many other uses not disclosed in so many words but which will be apparent to those familiar with the Practice of the art to which the invention relates. Furthermore, only those portions of a synchronized sound and moving picture system are shown in the drawing, as are considered necessary for a complete understanding of the invention.

Fig. 1 of the drawing shows, schematically, a combined sound and picture projecting system employing mechanical media sound records, mechanical-electric translators, vacuum tube amplifiers, and electro-magnetic sound reproducers.

Fig. 2 shows a coupling and switching device similar to that disclosed in Fig. 1, with the exception that in this case the coupling device is so designed that the impedances of the circuits connecting the amplifier and the mechanical-electric translators are at all times the same.

Fig. '3 illustrates a system of the same general character as that shown in either Fig. 1 or Fig. 2, but employing photographic sound records and photoelectric translating devices in place of the mechanical media sound records.

Fig. 4 shows a magnified section of arecord disc in which the sound is recorded in the form of a wavy trace of varying amplitude.

Fig. 5 shows a switching arrangement by which the potentiometers shown in Figs. 1, 2 and 3 may be reduced to half their size, and effect the same results.

Referring to Fig. 1 of the drawing. which sponding gears fixed to the respective shafts 6 and 7. When it is desired to produce a combined sound and moving picture program, commonly known as talking movies the stylus 21 is set at the beginning of the Acutting in record disc 18 and the driving motor M is started in operation. The spindle 10 carrying the turntable 16 is thereby opera- .tively connected with the main driving shaft thru the gears 12 and 14. For the present it will be assumed that the sound record to be reproduced, is divided into two portions and is carried by the disc records 18 and 19, the disc 18 carrying the first portion of the record, and the disc 19 carrying the remaining portion and likewise for the associated films. The electromechanical translating device 20 is now operatively associated with the record 18 by means of the stylus 21 which bears upon the record and follows the.spirally arranged sound cutting therein. The cutting as shown in Fig. 4 may be in the form of a wavy trace of constant depth, the amplitudes of the" trace corresponding to the intensity of the sound to be reproduced. In practice it has been found that the average amplitude of cutting varies from record to record. Unless special precautions are taken it may very well occur that when records having these different characteristics are used;

in succession, that the volume of sound emitted by the sound producer is at a different energy level for the successive recordsf Accordingly in systems of the prior art it has been customary to employ amplifiers having a variable gain which was required in many cases to be adjusted to correspond to the characteristics of the record being used. According to the present invention this extra adjustment is accomplished at the same time that the switchover is made from one record to another, as will appear hereinafter.

Returnin to the point where the turntable 16 is starte it will be assumed that the contact arm 22 of the potentiometer P, is in the position shown in Fig. 1. With the potentiometer so adjusted it will be seen that none of the current from the pick-up device 20 reaches the primary -winding of .the input transformer T, because of the shunt which is connected from conductor 23 to the electrical midpoint 25 of the. potentiometer P It is necessary therefore in order to effectively associate the device 20 with the amplifier A to adjust the potentiometer so that the contact 22 is above the midpoint 25. While this adjustment is being made the switch 27 is closed to connect the monitoring loud-speaker 28 or its equivalent in circuit. The contact 22 is then moved upwardly until the output of the vacuum tube amplifier A is at the proper level as indicated by the device 28. It is understood of course that the amplifier A has pick-up device from the amplifier, third to connect the other pick-up device to the amplifier, and fourth to gradually increase the currents reaching the input circuit of the amplifier until they reach the same level as for the disconnected record. Four distinct manipulations were necessary in --order to properly switch from one record to another. This switching in the system as shown in the drawing is effected in a single manipulation offcontact 22.

When the motor M has been started, as 'hezfeinbefore described, the contact 22 'is moved downwardly from its, previously set v "position, beyond the middle point 25. As

thisc'ontact 'is approaching the point 25 the potential applied to the primary winding of transformer is correspondingly reduced until the point 25 is reached when the applied potential is zero. As contact 25 moves downwardly beyond thepoint 25 the drop of potential through the potentiometer which is effective on transformer T is proportionately increased and the operator may continue moving the contact 22 until the device 28 registers the same output from amplifier A as was obtained with record 18.

From the foregoing description it is obvious that during the switching from record '18 to record 19, that at no instant is the input circuit of the amplifier A disconnected from either the device 20 or the device 31, and the gradual transition causes no disagreeable noises in the reproducer 29, such as are a necessary concomitant in systems where the switching necessitates an actual disconnection of the reproducer from the pick-up devices.

In the event that it is desirable to gradu ally fade the currents the device 20 into those from the device '31, the dotted conductor 24 is disconnected. Accordingly, the movement of contact 22 decreases. the effect of one pick-up while at the same time increasing the efl'ect of the other pick-up. I 1 i For example, with the contact 22 in the posi-'* tion shown, a circuit may be traced from the upper terminal of the primary winding of the transformer T, artificial line AL contact 22, section 33 of the potentiometer P, conductor 34, artificial line AL thru the device 31, and returning thence to the lower terminal of transformer T (primary winding). A corresponding circuit may be traced including the section 35 of potentiometer P, device 20, and the primary winding of transformer T. It will be noted however that the resistance of section 35 of the potentiometer is greater than that of section 33 and consequently the potential across winding 24 due to device 31 is correspondingly greater than that due to device 20. Actually the potentiometer may be of such a high resistance compared to the resistance of devices 20 and 31 that when the contact 22 is at the electrical mid-point of the potentiometer the potentials applied to the winding 24 are due to boththe device 20 and to the device 31. Consequently movement of contact 22 upward gradually decreases the potentials due to device 31 and at the same time, inan inverse sense, increases the potentials due to the device 20, this causes in the reproducer 29 a fading or blending of the effects of record 19.into those of record 18.

This last described fading feature is particularly useful in connection with so-called overlapping records, that is records having a portion of their cuttings duplicated. For example in the recording process the ending of the record in disc 18 may be duplicated in the beginning at disc 19. When records of this character are employed with the apparatus shown in Fig. 1, the switching operation from record to record may be accomplished withoutany interruption ofthe volume or character of the sound from the reproducer 29 thus giving to an audience the effect of a single continuous record.-

- It will be observed that in Fig. 1, artificial lines ALl, AL2 and AL3 are inserted between, the amplifier A and the transmitters 20 and 31. These lines serve the purpose of padding so that the impedance of the circuits looking from the amplifier and from the transmitters may be maintained constant and substantially independent of the particular position of the contact 22. Lines ALl, AL2 AL3 will correspondingly attenuate the currents-reaching the amplifier, and this attenuation ma in certain cases be objectionable, and may be eliminated by an arrangement such as disclosed in Fig. 2.

Fig. 2 shows a fader of the potentiometer type which combines the functions of both the potentiometer P and the padding networks shown in Fig.1. The potentiometer P2 of Fig. 2 may be of substantially low impedance enabling it to be mounted at the most convenient location from the stand oint of the picture rojector operator an at the same time e ecting a considerable reduction in cost. This potentiometer is connected to transmitters slmilar to those of Fig. 1 and is represented schematically by the rectangles.

36 and 37. By virtue of this potentiometer the impedance looking from the amplifier is .keptsubstantially constant and the impedances looking from the reproducers may be made to vary within certain prescribed limits. By this arrangement the losses resulting from the lines.AL -AL of Fig. 1 may be obviated.

For the purpose of connecting the input its movement it makes contact with one of the switch-points before breaking contact with the preceding point, thus insuring that the input circuit of the amplifier is not disconnected from the potentiometer when transition is made from one record to another. It will be observed that each switchpoint is connected to the potentiometer proper, thru a resistance 42, 43, etc., of such value that as a section of the potentiometer proper is re moved from the circuit the flow of impedance is maintained constant.

Under certain circumstances it may be desirable to build the potentiometer as an independent part of the amplifier in order that the switching mechanism 'may be located at the most favorable point from an operating view. For this purpose the spindle carrying the brush 39 is provided with a gear 45 which co-operates with a gear 46 fixed to the shaft 47. Shaft 47 is provided at its opposite end with a hand-wheel 48 which may be located at a point such that the switch may be manipulated by an operator without his leaving the picture projecting machine.

The method of switching from one record to another when using a switch and poten-- .Any well-known method may be employed for photographing the'sound variations on the films 49 and 58 as the particular formof photographic record to be used forms no feature of the present invention. Similarly, well-known means for feeding and guiding the films through their respective projecting machines are representeddiagrammatically 1 by the devices 50, 59 and 6.0. If desired the same projectingmachine may be used for both the sound and picture records in which case the sound record is prepared on the same film with the picture as is well known in the art.

In order that the varying transparencies "f the sound record on film 49 may be translated into corresponding current variations, a pickup is provided comprising an electrooptical system having the source of light 52,

a combination of lenses 53, 54, and a photo-- electric cell 56 or other light sensitive device. Light from the source 52 is .focussed by lens 53 upon the portion of the film 49 carrying the sound record. A light bafile plate 55 is provided between the lense 53 and the film in order to restrict the area of illumination thereof as is well-known in the art. The varying light transmitted by the film 49 is focussed by lens 54 upon the sensitive element of the cell 56 whose internal resistance is 'worrespondingly varied.- Accordingly the current flowing through the cell and the resistance 62, supplied by battery 61, follows the varying excitations of the cell 56. Resistance 62 is preferably ver high and of the order of the average wor ing resistance of the cell 56 in order that the varying currents from the battery 61 may cause relatively large changes in the potential drop across resistance 62 and corresponding changes in the potential of the grid 64 of the vacuum tube amplifier A which is coupled to the cell circuit by means of the couplin condenser 63. Amplifier A also serves to e ciently couple the very high resistance cell 56 with the relatively low resistance potentiometer P The amplified sound currents :are impressed by means of the transformer T2 upon the po-.

tentiometer P3 which may be of the type shown in either Fig. 1 or in Fig. 2. The contact arm of the potentiometer P3 is connected to the input circuit of-the fixed gain amplifier A3, whose output circuit is connected to the electromechanical reproducer 57.

Similarly another portion of the sound record is carried by film 58 which varies the light from the source 65 and the excitation of cell 66 to correspondingl vary the potential of the grid of the ampli er A2. The output of amplifier A2 is connected to potentiometer P3 as shown. When it is desired to switch from the record 49 to the record 58 the po-.

tentiometer contact is moved downwardly.

until the currents from cell 56 affecting the reproducer are reduced to zero and the currents from cell 66 are pro ortionately increased. If it is desired to ade one record into the other the conductor 68.is omitted and the currents from the cells 56 and 66 are simultaneously varied in inverse senses, giving 'n the reproducer the effect of a continuous record.

Fig. 5 shows a potentiometer and switch of the same general construction as the potentiometer P2 and switch S of Fig. 2. With the arrangement of Fig. 5 however only the upper half of the potentiometer P2 is required. Referring to Fig. 5, switch S is provided with additional segments 71, 72 and 73 which by means of brush 39 are bridged to the contact points 4.0, 41, etc. With brush 39 resting on contact 40 the voltages enerated by device 36 are applied to the full ength of the potentiometer resistance across which the amplifier 38 is connected, accordingly in this position of the switch the maximum volt ages are applied to the input circuit of the amplifier. As the brush arm is rotated counter-clockwise the potential drop through the potentiometer is gradually decreased thus correspondingly decreasing the volume of sound from the loudspeaker. When brush 39 is rotated to engage segment 73 the control of amplifier 38 is switched to the device 37 and continued rotation of brush 39 increases the potentials applied to the input circuit of the amplifier, until contact 74 is reached, when device 37 is connected across the full ,length of the potentiometer. Thus the same results are effected by potentiometer P4 as are effected by potentiometer P2 (Fig. 2) which later potentiometer requires twice as many sections as the former.

At this point it would be well to note that while it might be possibleto apply the currents from the photoelectric cells '56, 66

directly to the fader potentiometer P3, this arrangement would not be practicable for the reason that the photoelectric cell is inherently a very high resistance device and in order to -ment as disclosed in Fig. 3 comprising the vacuum tube A and the transformer T2. With the arrangement disclosed the potentiometer P3 may be located atthemost convenient point without fear of its being affected by outside interference.

From a consideration of the foregoing descriptions it is apparent that many modifica-- tions may be made in the apparatus disclosed without departing materially from the spirit and scope of the invention. For example the pick-up devices 20 and 31 may be replaced by such devices as telephone transmitters or any other source of voice modulated currents.-

Similarly any suitable means may be em- .ployed for varying the position of the potentiometer contact. It is also contemplated that the, potentiometer may consist of any I ords, variatlons from said records,

firm of electric impedance it being under? stood thatthe showing of Fi 1 in this respect is meant to be essentially so ematic.

Finally, while the invention for the purposes of description merel has been shown inconnection with a soun reproducing system, invention is not to be limited to such use, nor to the specific combinations of elements disclosed, but its scope is to be determined by the claims which are hereunto annexed.

What is claimed is:

1. In a transmission system, two sound rec means for producing series of electrical responding end portions of the first record corresponds with the beginning portion of the second record, a device for. translating said electrical variations into sound waves corresponding thereto, an adjustable potentiometer interconnecting said means and said translating device, and means to operate said potentiometer to render increasingly effective the electrical variations corresponding to the beginning of the. same'time increase one of said records and simultaneously to render decreasingly effective the electrical variations corresponding to the end portion of the other of said records, to pro uce in said translating device the efi'ect of an unin terrupted series of electrical variations.

2. In combination, a plurality of sound records, a pluralityof devices for translating into'corresponding electrical variations .the sound variations recorded on said-recs ords', a sound reproducer, associating said reproducer with said devices,.means' for adjustingsaid the effect or one potentiometer to. decrease of said devices on said reproducer and to at the effect of the other of said devices on said reproducer, the end of one of said records bearing a sound record identical with that appearing at the beginning of the second record whereby a shift from one translating device to the other may be made without being audibly perceivable. In testimony whereof, I have signed my name to this specification this 18th day of March, 1927,

' J. LOUIS REYNOLDS.

it is understood that the compass of the each series cor- I toa separate message to be trans mitted, said records being so related that the a potentiometer .for

simultaneously 

